1987-12-01_PERMIT FILE - C1981017 ‎(289)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Geotechnical Investigations Mine Portal Benches and Haul Roads
• Section_Exhibit Name: Chapter V Appendix V-E-II
• Media Type: D
• Archive: No

The geotechnical documentation of five mine benches in the
Coal Basin has been performed in a similar way. Configurations
of individual benches (cuts and fills) have been identified and
important geotechnical features documented. The methods of
documentation are described in detail in Appendix A.
Mine benches have a limited extent compared to the roads;
as topographic maps on a more detailed scale (1" = 200') were
made available to us , their documentation is presented on
separate Plates. Plates 4 through 7 present the documentation
of individual mine benches.
As part of the Phase 1 work, potential stability problem
areas have been defined. The potential stability problem areas
are road sections or portions of mine benches that may require
special reclamation procedures (to be estimated during
subsequent phases of this study) . The potential stability
problem areas are discussed in the last section of this report.
This section also includes our recommendations on the
reclamation test sections that are to be constructed in 1984
and monitored during the following years.
2. 0 SITE CONDITIONS
• 2. 1 GEOLOGIC AND MORPHOLOGIC CONDITIONS
The study area is underlain by sedimentary rocks of Upper
Cretaceous Age. Two important formations have been identified
in the area : the lower Mancos Shale and the upper , coal -
bearing , Mesaverde Formation. All haul roads have been
constructed within these two formations; the mine benches are
within the Mesaverde Formation only. Sedimentary rocks have
been penetrated by frequent vertical or subvertical dikes of
igneous rocks that have been mostly classified as the dacite
porphyry (occasionally, they closely resemble basalt) .
Mancos ' Shale and the Mesaverde rocks are the two
formations encountered in most coal mines of West and North
Colorado. Mancos Shale is a dark shale with a few interbedded,
thin layers of siltstone or sandstone. It occurs in thick beds;
bedding is not always clearly distinguishable in this
formation. Mancos Shale is known for its unfavorable physical
properties that include rapid disintegration and weathering of
the outcrops. It appears that the physical properties of Mancos
Shale in the Coal Basin are somewhat more favorable than in
other parts of Colorado; numerous rock cuts in Mancos Shale are
well stable even when excavated at very steep slope angles.
Mesaverde rocks are much more resistant to erosion than Mancos
Shale ; they are cliff-forming and retain steep to vertical
slopes. Mancos Shale usually forms flat slopes.
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